Glut4-mediated glucose uptake represents the rate-limiting step of insulin-stimulated glucose disposal, and type 2 diabetes is associated with impaired translocation of Glut4 to the cell surface. The insulin-responsive pool of Glut4 is localized in intracellular membrane vesicles, or IRVs, that deliver Glut4 to the plasma membrane. Proteomics analyses performed in our and other laboratories have shown that, in addition to Glut4, these vesicles contain three major proteins, sortilin, IRAP, and LRP1. Our hypothesis is that sortilin represents the "proactive" component of the IRVs which is responsible for their formation and insulin responsiveness, whereas other IRV proteins including Glut4 may just be "passive cargo" in this compartment. However, sortilin cannot perform its biological functions without regulatory proteins that interact with its cytoplasmic tail.
In Specific Aim 1, w propose to isolate and to identify these proteins by mass-spectrometry. Another important biological role of sortilin is to maintain normal levels of the Glut4 protein in adipocytes by retrieving it from endosomes. The specific mechanism of Glut4 retrieval is unknown and will be explored in Specific Aim 2. In addition to its role in the "Glut4 pathway", sortilin plays an important role in protein targeting from Golgi to lysosomes. In the previous funding period, we have found that sortilin interacts with adiponectin and facilitates its lysosomal degradation thus regulating adiponectin secretion at a previously unknown post-translational level.
In Specific Aim 3, we will test the hypothesis that sortilin targets adiponectin for degradation in lysosomes in an acyl CoA-dependent fashion.

Public Health Relevance

Impaired translocation of Glut4 to the cell surface represents the key factor for the development of type 2 diabetes mellitus. Recent studies point out to the cell biology of Glut4 recycling as a potential site of primary diabetes-related abnormalities. We propose to explore several unknown aspects of Glut4 traffic which will shed light on the molecular nature of insulin resistance and diabetes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
High Priority, Short Term Project Award (R56)
Project #
2R56DK052057-16
Application #
8845323
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Haft, Carol R
Project Start
1997-02-28
Project End
2015-06-30
Budget Start
2014-08-25
Budget End
2015-06-30
Support Year
16
Fiscal Year
2014
Total Cost
$163,700
Indirect Cost
$63,700
Name
Boston University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
604483045
City
Boston
State
MA
Country
United States
Zip Code
02118